In electronic apparatus such as telephones, radio telephones, radios, household appliances, meters, watches, etc., there are increasingly used functions the control and output of which require the use of an alphanumeric display as an information transfer channel between the apparatus and the user. The aim is to make the electronic apparatus small-sized and inexpensive. However, high requirements continue to be imposed on the display with respect to its clarity and readability. On the other hand, the same requirements apply to large-sized display devices, the largest being used in bulletin boards and in results or score boards in sports arenas.
A number of different display devices based on different matrix constructions are used in electronics today. For example, three different character types have been used in the radio telephones manufactured by the applicant. The oldest is the 7-segment display by means of which it is possible to form the numerals from linear elements in a familiar manner.
For use alongside the 7-segment display there is the 14-segment display, discussed below in greater detail, by means of which most of the alphabetic characters can be formed satisfactorily. Certain devices have 35-dot matrices by means of which beautiful alphabetic characters can be formed and which allow lower-case letters.
The importance of alphabetic characters has increased rapidly with the introduction of new functions the devices. The 7-segment display uses 8 bits of control, which can be obtained at two background levels. The 14-segment display also requires 4 signals and four background levels. Thus the contrast weakens physically to one-half, although this difference will not be as obvious to the plain eye. A 35-dot matrix requires as many as 7 background, levels and 5 signals. An improved form of character should support optical observation and fully compensate for the weakening of the contrast.
Problems appear in present-day displays when known segment displays and matrix displays are used. In the current era of digital watches, the 7-segment (FIG. 1) is familiar to everybody. Its readability is somewhat limited by the fact that several characters differ from some other character by only one element. The line in the character uses up 24-82 percent of the area of the figure, in which case the difference in comparison with the background remains clear.
In the 14-segment (FIG. 2), another 7 elements have been added inside the 7-segment. The coherence of the figures is broken, since at the corners there are three, and in the center as many as eight elements which control one and the same point. The plain eye will not perceive the figure easily, even if a numeral. The width of the line has to be narrowed at the ends of the lines, whereupon the darkness of the character is only 15-30 percent of the surface area of the figure. The 14-segment alphabetic characters do not have the same familiarity to the public as the numerals of the 7-segment display. The 14-segment is seen by the consumer only on certain self-service scales at markets. In the display on the scales the contrast has been increased by a great difference in brightness. Most of the alphabetic characters are therefore "guessable" in form.
The 7.times.5 matrix (FIG. 3) forms very beautiful numerals and does only a little violence to the forms of letters. Only the Scandinavian characters, as well as A, V, X and Y, are "difficult". Even in these, the matrix letter is familiar from, for example, results or score boards. The coverage is better than in the 14-segment, 20-80 percent, but the form is solid and clear, and therefore perception is easy, even if the character is physically weaker in a liquid crystal display. The matrix, however, requires larger and more expensive control electronics than do 7-segment and 14-segment displays.
From other contexts there are known matrix displays of other sizes also, for example 3.times.7, 5.times.3 and 5.times.5 matrix displays. Using the 5.times.3 matrix it is possible to implement, at least in principle, all alphanumeric characters. However, known applications are not capable of representing all letters satisfactorily.
The problems described above also apply to printers.